Helped my dad with the same issue afew weeks ago. What I did was first use some of the that foam bore cleaner. Spray it in there and let it sit in there for 20 minutes or so. Then take some patches and run them through it. When your patches come out dry, put more of that cleaner in there only this time take a wire brush and run that through the barrel acoupe times. Repeat these steps as many times as needed and check the barrel after each cycle of steps. Only took three cycles of doing that for me to get my dads optima back in workin condition.